The present invention relates to a precipitated silica, the process for the preparation thereof, and to its use in battery separators.
It is known to use precipitated silicas for the production of microporous polyethylene battery separators (U.S. Pat. No. 3,351,495, U.S. Pat. No. 4,024,323, U.S. Pat. No. 4,681,750). A common feature of the known silicas is that the salt produced during the precipitation reaction is removed from the filter cake during filtration to a salt content as low as &lt;2.5 wt. % by washing with water. The salt content of .ltoreq.2.5 wt. % refers to the salt content determined in the dried silica. In the filter cake, this corresponds to a salt content of 0.625% (see, for example, U.S. Pat. No. 4,681,750, column 8, Example 1, lines 20-23 and Table 1, Examples 1-3).
An object of the present invention is to reduce the amount of water needed to obtain an acceptable product. Another object is to lessen the amount of salt discharged with the effluent of the process. Further objects of the invention include obtaining improved products containing the precipitated silicas and improved processing of compositions containing precipitated silicas.